Background: The Austro-Asiatic linguistic family, which is considered to be the oldest of all the families in India, has a substantial presence in Southeast Asia. However, the possibility of any genetic link among the linguistic sub-families of the Indian Austro-Asiatics on the one hand and between the Indian and the Southeast Asian Austro-Asiatics on the other has not been explored till now. Therefore, to trace the origin and historic expansion of Austro-Asiatic groups of India, we analysed Y-chromosome SNP and STR data of the 1222 individuals from 25 Indian populations, covering all the three branches of Austro-Asiatic tribes, viz. Mundari, Khasi-Khmuic and Mon-Khmer, along with the previously published data on 214 relevant populations from Asia and Oceania.

Northeast India, the only region which currently forms a land bridge between the Indian subcontinent and Southeast Asia, has been proposed as an important corridor for the initial peopling of East Asia. Given that the Austro-Asiatic linguistic family is considered to be the oldest and spoken by certain tribes in India, Northeast India and entire Southeast Asia, we expect that populations of this family from Northeast India should provide the signatures of genetic link between Indian and Southeast Asian populations. In order to test this hypothesis, we analyzed mtDNA and Y-Chromosome SNP and STR data of the eight groups of the Austro-Asiatic Khasi from Northeast India and the neighboring Garo and compared with that of other relevant Asian populations. The results suggest that the Austro-Asiatic Khasi tribes of Northeast India represent a genetic continuity between the populations of South and Southeast Asia, thereby advocating that northeast India could have been a major corridor for the movement of populations from India to East/Southeast Asia.

Two different models of diffusion-demic and cultural-have been proposed as an explanation for the spread of languages. Recent studies have shown that in some cases the dispersal of the language was due to the demic diffusion while for others it is purely due to the process of acculturation. There are four major linguistic families in India which have largely their own geographic domain. However, there are a few situations in which the populations affiliated to different linguistic families cohabit. For example, we find the spread of the Indo-European and Dravidian tribal populations in the core/peripheral areas of the Mundari Austro-Asiatic groups. These non-Mundari groups have been termed as transitional populations to indicate that these populations originally were probably Mundaris. However, there has been no attempt to ascertain if these populations are genetically Austro-Asiatics or do they belong to the linguistic groups that they are currently affiliated to. To examine this we have analysed Y-SNPs and STRs data of the 13 Mundari and 7 transitional groups and compared with the other populations of relevant linguistic groups. The results suggest that the Indo-European transitional groups are genetically Mundari and have acquired the present language through the process of cultural diffusion, while in the case of Dravidian transitional groups, the spread of language seems to be due to the process of both, the demic and cultural diffusion.

We report single nucleotide polymorphisms (SNPs) at the four sites in ADH2 and ADH3 genes among the 28 populations from southern parts of Andhra Pradesh, India. A total of 1048 individuals belonging to 28 endogamous populations distributed in the contiguous areas of the 6 southernmost districts of Andhra Pradesh were enrolled for the present study. Genotyping involved PCR and sequencing. We sequenced exon 3 and 9 of ADH2 and exon 8 of ADH3, besides the ADH2 3'UTR-rs17033 (72 bases down stream of ADH2 Arg369Cys). The two sites of ADH2 (Arg47His and Arg369Cys) are found to be completely monomorphic showing only Arg47 and 369Arg (ADH2*1 allele), the remaining two sites were polymorphic. None of the 28 populations of this study deviated significantly from Hardy Weinberg Equilibrium proportions. The allele frequencies do not show any clear trend across socioeconomic groups. The degree of heterogeneity in the genotype frequencies among the hierarchical groups is significant for Ile349Val (df = 12; χ 2 = 22.050) and not for the 3'UTR rs17033 (df = 6; χ 2 = 9.765). The haplotype distribution among the hierarchical groups is found to be highly homogeneous and statistically nonsignificant (χ 2 = 0.248, df = 18). Linkage disequilibrium does not exist between the two-polymorhic loci. The results were interpreted in the light of cultural patterns of the Indian hierarchical society.

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